This is Robert Lamb's simpliest version of the
meter circuit which can be attached to the
Hall circuit he designed. I use mine on a continuious
running basis switched to the + -
3 volt scale reading.
The other .3 volt and .03 volt outputs can be useful
in determining circuit drift amounts
over time. He has used these with and without
the Hall magnets, and with and without shielding around the hall itself,
which in itself can be very interesting elements to consider when you may
wish to build your own version. Actually, by this method, he was
able to determine that by replacing the original voltage regulators (78L05
5 volt positive regulator)
and the 79L05 5 volt minus regulator, with the new
National Semiconductor LM236-5.0 volt reference device, that the drift
was greatly reduced. Additionally, by only using the meter circut,
aspects like oscillation could be mostly resolved by soldering in potential
elements like capacitors in various places and then watching the meter
circuit for total span reductions over time. Yes...amazing stuff
to watch for me, but old hat too him-ha.
The meter on the circuit above is a + - 25 microampere
unit (25-0-25). We got ours from "The Electronic Goldmine" (A Arizona
based, web only, electronic surplus store), for ~ $6.00 plus shipping etc.
Its a Weston brand plastic unit with a snap on plastic backing. Of
course if you already have an older working commercial meter type voltmeter,
you won't need the above meter circuit, unless you want it.
This pages last update is 10/15/98